We have an issue with signins not working on the dev.twitter.com site at the moment.

In the meantime, I would recommend that you look at using twurl to test any requests you need rather than attempting to use the OAuth Generator tool. There's a tutorial available if you're not familiar with that tool.

Signins are still not working on dev.twitter.com at the moment, however, there should only be one or two reasons for this to cause a problem - access to restricted content (which should not affect the vast majority of non-Twitter employees), or use of the OAuth generator tool. We recommend using another tool like twurl instead. If you need to access your apps, apps.twitter.com is unaffected.

I don't have any eta for the meta issue to be resolved at the moment - low priority since there are alternatives.